1. Field of the Invention
The present invention relates to an apparatus for indicating the change in position of the drawworks drum in a drilling rig, and more particularly, to an apparatus for determining and displaying such drilling related parameters as rate of penetration of bit and traveling block position.
2. Description of the Prior Art
In an oil well drilling rig, a traveling block is suspended from a crown block by means of a cable having one end secured at a suitable location on a derrick and the other end wrapped around a rotatable drumworks drum. A drilling apparatus is coupled to the traveling block and extends into a drill hole. As drilling proceeds, the drawworks drum rotates thus lowering the traveling block. The drilling apparatus coupled thereto penetrates the earth's surface at a rate which is determined by a number of variables. To facilitate control of drilling operations, it is desirable to monitor and record the position of the traveling block, as well as other parameters.
U.S. Pat. No. 4,419,886 to Peterson describes a number of prior art methods of obtaining the desired traveling block position information. Those methods include use of a measuring line directly connected to the traveling block, use of drum rotation measuring systems including electronic means for compensating for various diameters of material wound about a drum, and use of pneumatic devices to measure movement of the traveling block. The descriptions in U.S. Pat.No. 4,419,886 of those prior art methods, as well as the associated descriptions of the shortcomings of each of those prior art methods, are incorporated herein by reference.